There is mounting clinical and laboratory evidence that the flexure of the dental crown following intracoronal composite shrinkage may be related to a number of clinical and biological phenomena, including early dentin bond failure, crack initiation and propagation, and possibly post-operative symptoms. A major goal of this proposal is the determination of the extent and possible clinical significance of these effects in an in vitro experimental model with servohydraulic control and direct strain read out from intact and restored human teeth. The hypothesis to be tested is that polymerization contraction of composite restorative materials results in decreased longevity of the restoration due to internal stress development, early dentin bond failure, alterations in occlusal contacts, and crack initiation and propagation of the natural tooth structure. The biomechanics of composite polymerization kinetics and its effects on tooth structure will be investigated by: 1) strain gage characterization of polymerization contraction strain and stress, 2) evaluation of the deformation of the composite restored tooth through strain gage measurement, 3) evaluation of the response of the composite restored tooth during simulated occlusal loading in an artificial mouth and 4) validated finite element analysis of the restored tooth complex. It is hoped that these studies will increase the knowledge base of the biomechanical interactions internally, at significant boundaries and on the surface of the restored tooth complex. From this, new criteria in materials development can be determined and a sounder basis for materials choice, treatment planning, and fabrication of intracoronal restorations can be developed.